1. Field of the Invention
This invention relates in general to spin valve heads for magnetic storage systems, and more particularly to a method and apparatus for enhanced giant magnetoresistance (GMR) effects using positive magnetostrictive material embedded in a self-pinned composite layer.
2. Description of Related Art
Magnetic recording is a key and invaluable segment of the information-processing industry. While the basic principles are one hundred years old for early tape devices, and over forty years old for magnetic hard disk drives, an influx of technical innovations continues to extend the storage capacity and performance of magnetic recording products. For hard disk drives, the areal density or density of written data bits on the magnetic medium has increased by a factor of more than two million since the first disk drive was applied to data storage. Since 1991, areal density has grown by a 60% compound growth rate, which is based on corresponding improvements in heads, media, drive electronics, and mechanics.
Magnetic recording heads have been considered the most significant factor in areal-density growth. The ability of the magnetic recording heads to both write and subsequently read magnetically recorded data from the medium at data densities well into the Gigabits per Square Inch (Gbits/in2) range gives hard disk drives the power to remain the dominant storage device for many years to come.
Important components of computing platforms are mass storage devices including magnetic disk and magnetic tape drives, where magnetic tape drives are popular, for example, in data backup applications. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an Air-Bearing Surface (ABS) between the slider and the rotating disk. The suspension arm biases the slider into contact with the surface of the magnetic disk when the magnetic disk is not rotating. However, when the magnetic disk rotates, air is swirled by the rotating disk adjacent to the ABS causing the slider to ride on a cushion of air just above the surface of the rotating magnetic disk. The write and read heads are employed for writing magnetic data to and reading magnetic data from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A magnetoresistive (MR) sensor detects magnetic field signals through the resistance changes of a sensing element as a function of the strength and direction of magnetic flux being sensed by the sensing element. Conventional MR sensors, such as those used as MR read heads for reading data in magnetic recording disk and tape drives, operate on the basis of the anisotropic magnetoresistive (AMR) effect of the bulk magnetic material, which is typically a perm-alloy. A component of the read element resistance varies as the square of the cosine of the angle between the magnetization direction in the read element and the direction of sense current through the read element. Recorded data can be read from a magnetic medium, such as the magnetic disk in a magnetic disk drive, because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the read element, which in turn causes a change in resistance of the read element and a corresponding change in the sensed current or voltage.
In the past several years, prospects of increased storage capacity have been made possible by the discovery and development of sensors based on the giant magnetoresistance (GMR) effect, also known as the spin-valve effect. In the spin valve sensor, the GMR effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium, or signal field, causes a change in the direction of magnetization of the free layer, which in turn causes a change in the resistance of the spin valve sensor and a corresponding change in the sensed current or voltage.
Magnetic sensors utilizing the GMR effect are found in mass storage devices such as, for example, magnetic disk and tape drives and are frequently referred to as spin-valve sensors. The spin-valve sensors being divided into two main categories, the Anti-FerroMagnetically (AFM) pinned spin valve and the self-pinned spin valve. An AFM pinned spin valve comprises a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the pinned layer because it is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent AFM layer, commonly referred to as the pinning layer, which pins the magnetic orientation of the pinned layer through anti-ferromagnetic exchange coupling by the application of a sense current field. The other ferromagnetic layer is called the free or sensing layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields.
In the self-pinned spin valve, the magnetic moment of the pinned layer is pinned in the fabrication process, i.e.xe2x80x94the magnetic moment is set by the specific thickness and composition of the film. The self-pinned layer may be formed of a single layer of a single material or may be a composite layer structure of multiple materials. It is noteworthy that a self-pinned spin valve requires no additional external layers applied adjacent thereto to maintain a desired magnetic orientation and, therefore, is considered to be an improvement over the anti-ferromagnetically pinned spin valve.
In spin valve sensors that provide exchange coupling with an AFM layer, several problems exist. The exchange field strength, for example, of a Fexe2x80x94Mn AFM pinning layer is highly sensitive to temperature. As the temperature increases, the Fexe2x80x94Mn pinning layer is said to soften, whereby the Fexe2x80x94Mn pinning layer""s ability to fix the magnetization of the ferromagnetic pinned layer decreases. Thus, any Electro-Static Discharge (ESD) event, which causes an increase in temperature, may reduce the pinning capability of the Fexe2x80x94Mn pinning layer.
Additionally, the use of Fexe2x80x94Mn requires careful control of the fabrication process steps and the use of protective materials as Fexe2x80x94Mn is highly susceptible to corrosion. Further, the use of Fexe2x80x94Mn also requires that the anti-ferromagnetic material used to exchange bias the free ferromagnetic layer be made of a different material, such as Nixe2x80x94Mn. To provide sufficient exchange coupling field strength, however, the Nixe2x80x94Mn must be annealed, which may cause interdiffusion of other materials into the free layer causing decreased magnetoresistance and other detrimental effects.
Prior art self-pinned spin valves, seeking to eliminate the problems of the AFM exchange coupled spin valves, provide an Anti-Parallel (AP) laminate structure consisting of first and second Ferromagnetic Pinned (FP) layers separated by an Anti-Ferromagnetic Coupling (APC) layer. The magnetic orientations of the first and second FP layers are set to be in opposite directions and the thickness of the FP layers is such that the net magnetic moment of the laminated structure is near zero. In order for the intrinsic anisotropy field (Hk) of the AP laminate structure to remain self-pinned, the magnitude of Hk must be several times larger than the coupling field of the free layer. Depending upon the materials used for the FP and APC layers of the prior art, a preferred minimum thickness of the APC layer is desired in order to strengthen the anti-ferromagnetic coupling between the AP layers. The thickness of the APC layer may be made so thin, however, that pin holes are introduced into the APC layer, which affect the coupling strength of the APC layer.
It can be seen therefore, that there is a need for an improved, self-pinning spin valve structure which eliminates the problems of the AFM exchange coupled spin valves and also increases the pinning strength of the AP laminate structure of the prior art without the necessity of adjusting the thickness of the APC layer.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for increased pinning strength of an AP layer through the use of an embedded, positive magnetostrictive material between outer layers of ferromagnetic material. The present invention increases the pinning strength of the self-pinned AP layer by increasing the perpendicular to ABS Hk, which enhances both the intrinsic and the stress induced uniaxial anisotropy field.
A method in accordance with the principles of the present invention includes forming a first pinned layer having a first magnetic orientation on a substrate. The method of forming the first pinned layer includes embedding an inner ferromagnetic layer between first and second ferromagnetic layers. The inner layer providing a greater positive magnetostrictive coefficient in relation to the first and second ferromagnetic layers. The method further comprises depositing a second pinned layer having a second magnetic orientation above the first pinned layer. The first and second magnetic orientations are self-biased anti-parallel in relation to one another.
In another embodiment of the present invention, a spin valve sensor is provided. The spin valve sensor includes a first pinned layer having a first magnetic orientation. The first pinned layer including a first ferromagnetic layer, a second ferromagnetic layer disposed above the first ferromagnetic layer, and an inner ferromagnetic layer embedded between the first and second ferromagnetic layers. The inner ferromagnetic layer having a greater positive magnetostrictive coefficient in relation to the first and second ferromagnetic layers. The spin valve sensor further comprises a second pinned layer having a second magnetic orientation. The first and second magnetic orientations are self-biased anti-parallel in relation to one another.
In another embodiment of the present invention, a magnetic storage system is provided. The magnetic storage system includes a magnetic recording medium and a spin valve sensor disposed proximate to the recording medium. The spin valve sensor comprises a first pinned layer having a first magnetic orientation. The first pinned layer including a first ferromagnetic layer, a second ferromagnetic layer disposed above the first ferromagnetic layer, and an inner ferromagnetic layer embedded between the first and second ferromagnetic layers. The inner ferromagnetic layer having a greater positive magnetostrictive coefficient in relation to the first and second ferromagnetic layers. The magnetic storage system further comprises a second pinned layer having a second magnetic orientation. The first and second magnetic orientations are self-biased anti-parallel in relation to one another.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity to the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.